The present invention is directed to stabilized compositions of particulate materials and the use of such compositions to remediate contaminants from soil and groundwater.
There are many useful remediation agents for removing organic and inorganic contaminants from groundwater. Such agents can operate in a variety of modes including through sorption, direct destruction, stimulation of biodegradation and/or through stabilization of the contaminants. Through these various modes of action, the remedial agents act to detoxify the water and reduce any health risks associated with the contaminant.
While some remedial agents are completely soluble in water and allow for their relatively straightforward application in both in place (in situ) and out of place (ex situ) systems, many useful remedial agents are not soluble in water. In these cases, the application of the insoluble remedial agents is often limited to above ground treatment systems (e.g., pump and treat systems) or in trench barriers (e.g., permeable reactive barriers). However, it is desirable to use these solid remediation agents in situ and apply them via various injection or percolation techniques in order to increase the range of sites that can be treated and to reduce project costs.
The limitation with solid remedial agents is that they are commonly manufactured in granular or powdered forms and therefore lack mobility in the subsurface which limits their contact with contaminants and the efficacy of treatment. The lack of mobility requires installation techniques that are more expensive, more disruptive to the subsurface, and often render less control of emplacement; an example of this is high pressure injections (e.g., hydraulic fracturing or fracking). Even if the solids are manufactured in a smaller particle size, they tend to agglomerate and then still require similar disruptive injection techniques.
For example, the use of metal sorbents, particularly materials that are derived from or contain apatite-type phosphate minerals, is an established method for remediating water and soil contaminated with metals or radionuclides. Several of these materials may include hydroxyapatite, bone char, and apatite II, among others. The apatite-containing materials can capture or chemically immobilize metals and radionuclides as insoluble forms with extremely low solubility constants to reduce their bioavailability and decrease human and ecological risks by removing them from the dissolved phase and preventing their migration.
Typically, these materials are used in granular or powdered form within above ground treatment systems or they can be emplaced in situ via various physical methods e.g. soil mixing, back-filling of excavations, fracking, or installing in trenches known as permeable reactive barriers. These relatively disruptive application methods are required for apatite-based materials in powder or granular form because they do not readily distribute through soil to reach areas of contaminated water. This lack of mobility causes the cost of treatment to be very high, whereas the contact with contaminated water remains quite low. The high cost is primarily due to the installation requirements to thoroughly treat a contaminated area.
Exemplary prior art teachings of metal sorbents for use in metals remediation include the following references:
Tofe, U.S. Pat. No. 5,711,015, Filed 1996. Discloses the use of pulverized or particulate animal bone or synthetic bone as a source of hydroxyapatite to decontaminate various metals (transuranic, Pu, radioactive). Discloses the use of <0.1 mm to 10 mm sized particulates. Discloses the method of passing metal contaminated water through a container that holds the hydroxyapatite-based particulates.
Conca & Wright, U.S. Pat. No. 6,217,775 B1, Filed 1998. Discloses the use of fish bones and fish hard parts with associated organics in order to treat soil leachates or waste sites contaminated with various metals (lanthanides, actinides, Pb, Zn, Cu, Cd, Ni, U, Ba, Cs, Sr, Pu, Th). Discloses methods for using the material that includes backfilling an excavation, horizontal drilling,
Moore, U.S. Pat. No. 6,416,252 B1: Discloses a method for in situ formation of apatite barriers by injecting precursor reagents, ex. sodium phosphate and calcium chloride, into the subsurface. Also discloses optimal pH ranges of 7 to 8 and optimal temperatures of 40° C. to 100° C. for this process.
In another example, activated carbon is commonly used as a sorbent medium for removing organic and inorganic contaminants from water. It is used in treatment systems to detoxify industrial process water, as well as in pump-and-treat systems for above-ground treatment of contaminated groundwater. In use, activated carbon is typically manufactured and used in granular or powder form whereby the particulate is loaded into fluid- or fixed-bed treatment systems or dispersed or distributed over the area subject to contamination.
The in situ application of activated carbon to soil and groundwater allows for the capture or immobilization of contaminants from groundwater via sorption onto the carbon. This inhibits the migration of a contaminant plume and lowers the risk of damage to human health or ecological systems. Exemplary prior art teachings of carbon-based compositions for use in environmental remediation include the following references:
U.S. Pat. No. 4,664,809, issued May 12, 1987, to Fenton, entitled GROUNDWATER POLLUTION ABATEMENT, discloses drilling of wells in the ground and injecting a sorbent for contaminants into the path of groundwater plume, in order to stop the plume. Such reference further discloses the use of activated carbon as a sorbent and the addition of stabilizing substances to sorbent slurries.
In the name of Kopinke, F.-D.; Woszidlo, S.; Georgi, A., European Patent Application EP 1462187 A2, filed Mar. 2, 2004, “Verfahren zur in-situ Dekontamination schadstoffbelasteter Aquifere,” discloses a process for in-situ decontamination of polluted aquifers—by injection of colloidal carbon. Such reference discloses that a charcoal particle size <10 microns is optimal and that ionic strength inhibits colloid transport. The objective of the invention is to increase distribution of carbon colloids in subsurface by flushing with deionized water or raising pH of aquifer.
Georgi, A.; Schierz, A.; Mackenzie, K.; Kopinke, F.-D., Terra Tech, 2007, 16, (11-12), 2-4. “Mobile Kolloide. Anwendung von kolloidaler, Aktivkohle zur In-Situ-Grundwasserreinigun, (in German) also refers to aquifer treatment with colloidal activated carbon and that a 0.1 to 10 micron activated carbon particle size is needed for stability and mobility. The optimal particle size is disclosed as 0.5 to 2 microns. Moreover, such reference teaches that humic acid and carboxymethylcellulose (CMC) are stabilizers of activated carbon colloids and can have a max loading of <10% on carbon.
Mackenzie, K., et al.; Water Research 2012, entitled “Carbo-iron—An Fe/AC composite—As alternative to nano-iron groundwater treatment” and supporting information is a paper teaching the use of “carbo-iron” an activated carbon material that has embedded iron metal particles for contaminant treatment. The carbo-iron is comprised mostly of activated carbon and behaves similarly to activated carbon as a colloidal material. Such reference discloses that max loading of CMC onto carbo-iron is 7% w/w and that no further stabilization benefit occurs above 5% w/w loading of CMC.
The prior art Georgi (2007) and Mackenzie (2012) references referred to above disclose that sodium carboxymethyl cellulose (a polyanionic polymer) stabilizes colloidal activated carbon against settling. It also has some effect to increase transport of activated carbon through soil and groundwater in situ. As the carbon contacts the contaminated groundwater, contaminants are sorbed out of solution and onto the carbon particles. Carboxymethyl cellulose-stabilized colloidal carbon can also transport somewhat in the aquifer, but is destabilized and deposited by ionic strength of the water (Kopinke 2004).
There are additional examples that describe the use of carboxymethyl cellulose to stabilize and enhance the transport of mobility limited nano- or colloidal-sized remediation agents. An example of this is with zero valent iron (ZVI) that is described in U.S. Pat. No. 7,635,236 issued to Zhao and Xu on Dec. 22, 2009, entitled “In situ remediation of inorganic contaminants using stabilized zero-valent iron nanoparticles.” This patent discloses the use of CMC to control the dispersivity of ZVI to remediate inorganic toxins.
The mobility limitations described for activated carbon, apatite-containing materials, and ZVI above are inherent to insoluble remediation agents. And while the use of CMC has been established to enhance these types of materials, there is still a desire to enhance the transportation of the materials in situ where they will interact with the natural ionic strength of groundwater.
The teachings of all the aforementioned references are incorporated herein by reference. Notwithstanding their respective teachings, however, there are significant limitations regarding the use and efficacy of in situ treatments. In particular, as a powder or granular material, remediation materials, such as activated carbon, cannot distribute through soil to reach areas of contaminated water. Instead, it must be applied in a trench to treat water passing therethrough, or must be injected as a slurry which has limited or no mobility in the aquifer. This lack of mobility causes the cost of treatment to be very high, whereas the contact with contaminated water remains quite low. The high cost is primarily due to the large number of application points required to thoroughly treat a contaminated area.
To facilitate treatment of contaminated groundwater, it is desirable that the remediating agents be able to transport effectively through an aquifer to reach contaminated zones while remaining highly active toward contaminants. To facilitate treatment of contaminated groundwater, it is desirable to have a form of solid remedial materials that can be emplaced in situ with minimal disturbance to the native aquifer conditions and that can transport effectively through an aquifer to reach contaminated zones while retaining its treatment efficacy. Additionally, the remediating agent should be effective across a wide range of aquifer conditions, including pH and redox.
It is therefore desirable to have improved methods and compositions that will distribute colloidal remediation agents, including those treating organic and inorganic contaminants (e.g., chlorinated solvents, pesticides, energetics, hydrocarbons, metal contaminants, etc.), much farther in the subsurface than simple carboxymethyl cellulose. It is likewise desirable to provide such a composition that is of simple formulation, easy to deploy, is substantially effective at remediating contaminants from soil and groundwater, and is further substantially more effective in becoming dispersed and capable of being quickly and effectively deployed over a greater area of volume of soil and groundwater than prior art compositions and methods of using the same for environmental remediation.